The invention refers to oscillating or reciprocating apparatus for a strand casting mold which is movable in a guide parallel with the strand vein and whose oscillatory movements are transmitted by means of rocking levers from a motor. This type of oscillating apparatus serves to loosen the liquid metal to be cast, particularly liquid steel, from the wall surfaces of the strand casting mold during the solidification process. In general, sinusoidal oscillatory motions or variations of the sine shape and/or variations of amplitude are provided for differential up and down movements.
The means producing the oscillatory motions consist generally of an electric motor driving an eccentric shaft connected to rocking levers. Due to the remote connection of the electric motor, there is a multitude of moving joints. All known oscillating devices use sprocket chains of considerable length. Of disadvantage in this type of apparatus is the great expenditure for the complicated lever gears and for the lever rotary gears, causing inaccuracies in the oscillatory path. In order to repeat exactly the required movements for the strand casting mold, accurately working lever gears are necessary.
The great number of parts also makes such oscillating and/or reciprocating devices very susceptible to disturbances; they are not easily accessible and difficult to service, and finally, they only offer a small degree of operating safety in the rough operation of a foundry. German Patent Publication DE-OS No. 25 46 689 shows an example of such an oscillating device.
Contrary to the prior art, the present invention provides an oscillating apparatus without the described disadvantages, which can function with very short sprocket chains, thus requiring little expenditure, and simultaneously, processing the characteristic of exactly maintained paths of motion and of operating with greatest possible safety. The invention solves this by providing the support points between the strand casting mold and/or the lift table carrying it and the rocking levers with elastic and/or resilient supporting elements surrounding the articulated axle, by providing as rocking levers two-arm levers pivoting around rotary axes, and by connecting these with the other lever arm on each strand side to draw and/or thrust rods joined to the rocker gear. Expenditure is primarily reduced on account of the hinging of the two-arm levers to one common draft element. Furthermore, the power transmission path starting at the rocker gear is considerably shortened. The shorter power transmission path, in turn, reduces the number of sources of error so that the paths of motion are maintained more accurately than heretofore.
The greatest degree of accuracy, however, is achieved by means of the supporting elements surrounding the articulated axle. The looseness or play occurring in known lever gears is prevented by means of the resilient supporting elements. The chain of power from the electric motor via a series gear with a following eccentric shaft can, therefore, be almost free of play during the entire oscillatory motion. Furthermore, it is advantageous that the elastic supporting elements permit heat expansion processes of the strand casting mold and/or lift table on which the mold is arranged, symmetrically with the strand axis, without exerting pressure on the casting strand.
Pressure resulting from lever pairs of uneven length for curved motions is eliminated by hinging an additional lever at a rocking lever pair on both sides of the strand vein between the lever carrying the elastic supporting element and the mold and/or lift table. A space-saving arrangement of the oscillating apparatus is achieved by providing toggle levers as two-arm rocking levers.
According to the basic concept of the invention, the oscillating or reciprocating apparatus is suitable for straight as well as curved strands. For curved strands, the lever arms carrying the elastic supporting elements are of even length within one pair, and the pairs are of differential lengths. Furthermore, it is advantageous that the draw and/or thrust rods next to the strand vein may be adjusted in length. This makes it possible to adjust, without play, the initial positions of the rocking levers with reference to the strand casting molds and/or with reference to the lift table carrying the strand casting mold.
According to another improvement of the invention aiming at a favorable power transmission path, the draw and/or thrust rods are hinged by means of joints to other draw rods and/or to the two-arm levers and to the rocker gear. For the adjustment of the two-arm rocking levers, it is also advantageous that in the draw and/or thrust rods provided in pairs each rod is adjustable in length. Another detail of the invention provides that the means for adjustment of the length of a draw and/or thrust rod consist of a turn-buckle, an expansion bolt or the like.
The accuracy of the lever system is also furthered by arranging the pillow blocks receiving the rotary axes for the rocking levers on a common supporting frame. The basic idea of this measure is to obtain an even greater accuracy, with respect to the symmetrical arrangement and thus the synchronism on each side of the strand vein. The parallelism of the rocking levers is also of considerable importance for the oscillatory motion to be produced.
The invention also relates to safety measures for the strand casting operation. Here we start with pressures caused by heating of the lift table and/or the strand casting mold, so that heat expansion forces might affect the rocking levers, the elastic supporting elements, and the draw rods. The invention provides that the pillow blocks are displaceable on the supporting frame in horizontal direction of the strand vein. This direction essentially corresponds to the direction of the casting strand, also if curved shape is projected onto a horizontal plane.
As a counter-measure to the solidification of a casting strand in the upper areas of the supporting roller stand, exerting pressures on its supporting elements, it is further provided that the supporting frame be displaceable along a guide extending in a horizontal plane in the direction of a curved vein. For safety reasons, it is also advisable that all assemblies of the oscillating gear, with the exception of the motor, are secured on the supporting frame. Usually the motor is affixed with a disconnect coupling at the series gear for the eccentric shafts, so that a heat expansion force effective in the strand vein direction and/or a force resulting from the contraction behaviour during the cooling of the cast strand, can easily be intercepted by loosening the coupling when displacing the supporting frame.
According to the invention, the starting basis for the interception of pressures from the support roller stand is the fact that consoles are provided on the supporting frame to accommodate the first group of strand support elements pertaining to a strand guiding arrangement following the strand casting mold. Pressures which may result from the contraction of the cast strand are now intercepted, according to the invention by providing on the console the bearing for the first group of strand support elements displaceable in the horizontal direction of the strand vein. An initial interception of heat expansion and/or heat contraction forces may therefore take place between the first group of strand support elements and the supporting frame for the assemblies of the oscillating gear.
In addition to the elastic support elements surrounding the articulated axle of the rocking levers, the supporting and/or rotary bearings of the two-arm rocking levers consist of elastic support elements which are rotary-elastically seated in sleeves. As far as the lift table together with the strand casting mold exerts heat expansion pressures on the rocking levers which can no longer be intercepted at the support points between the strand casting mold and/or the lift table carrying it, and the rocking levers, the supporting and/or rotary bearings of the two-arm rocking levers are also capable of receiving such pressures. Also, the articulated axle, the elastic support element, and the sleeve form an interchangeable structural unit.
The rotary elasticity of the elastic support elements is utilized to build an initial stress force acting against the weight force of the lift table and/or the strand casting mold, by installing the elastic support elements in the two-arm levers at least within the rotary bearings of the pillow blocks in operating position with a restoring or return force.
The invention further includes attaching to the strand casting mold and/or the lift table and the pillow block a flexible draft element, invariable in length, which is directed toward the center of curvature if the course of the strand is curved. This provides another means for increasing the accuracy of a curve guide during up and down swinging of the lift table together with the strand casting mold. Several of this type of draft elements may be provided. Another detail of the invention provides the flexible elements with initial stress, also to support the accuracy of the swinging movements.
It is also advantageous with respect to the accuracy of the vibration process that the flexible draft elements adhere at the end of the oscillating path to a roll-off surface adapted substantially to the bending line, in order to guarantee the desired distance from the center of curvature at any angle setting of the vibratory motion. The distance is in most cases the same. However, it may also assume a curved path deviating from the circular motion, according to the invention.